Multiple frequency antenna system



July 16, 1963 w. E. at VRAlN YETAL 3,

MULTIPLE FREQUENCY ANTENNA SYSTEM Filed July 18, 1960 United States Patent 3,098,231 MULTIPLE FREQUENCY ANTENNA SYSTEM Wallace E. St. Vrain, Kirl-rwood, and Curt A. Locke, St- Jolms, Mo., assignors to Mosley Electronics, line, Bridgetou, Mo., a corporation of Missouri Filed July 18, 1960, Ser. No. 43,448 4 Claims. (Cl. 343-745) This invention relates to improvements in antenna systems and, in particular, is concerned with a multi-frequency antenna system whereby different preselected frequencies can be either transmitted or received.

There has existed in the radio communication art a definite need for multiple frequency antenna systems. Thus, in many instances it is desirable to be able to either receive or transmit upon multiple frequencies. This is true in police, military, civil, and amateur communication systems. In such systems it is desirable to be able to either receive or transmit automatically upon such multiple frequencies without the necessity of changing the antenna length or making other adjustments in the antenna system.

Attempts have been made to provide such multiple frequency antenna systems and one such embodiment is shown in the Pichitino Patent No. 2,898,590. This patent shows a system for receiving three preselected frequencies. However, it is not possible to effectively receive more than three in the system so shown.

By means of the instant invention there has been provided a multiple frequency antenna system which makes it possible, by means of the tuning system herein provided, to receive very effectively four and five separate frequencies without further tuning once the antenna system has been set up. Essentially, the antenna tuning system of this invention contemplates the use of a short antenna, approximately one-quarter wave length, at the highest frequency, which operates on resonance at four and five and even more separate frequencies. The principle of operation is based on the property of a series resonant circuit offering low impedance at resonance and a high impedance at anti-resonance combined with a parallel resonant circuit operating in the opposite manner. Essentially, this is made possible by providing an impedance coil and a number of series resonant circuits connected in parallel with the coil and a parallel resonant circuit connected in series between the impedance coil and the series resonant circuits and which may be termed an isolating circuit. The isolating circuit has the very decided advantage that makes possible the receiving or transmitting of more than three separate frequencies by means of the tuning system of this invention.

Accordingly, three has been provided, by means of this invention, a simply designed multiple frequency antenna system. This antenna system can be conveniently employed at the base of the antenna for mobile operation. Thus, the antenna tuning system can be used in a transportation vehicle, such as a car or the like, to receive multiple frequencies such as four, five, or even more separate frequencies. The tuning system may be very conveniently set up to operate on a fifty ohm unbalanced line which may be connected from the antenna tuning system to the ground system in a car and connected by a coaxial cable to the car radio system. In addition, the conventional amateur wave length bands can be very simply tuned by means of the tuning system of this invention and, as an example, the ten, fifteen, twenty, forty and eighty meter wave lengths can be very advantageously obtained by maintaining the antenna on resonance and ready to operate on any of these bands, but it is to be understood that the frequencies so tuned are not confined to the amateur bands.

The tuning system is one that can be easily installed in a conventional antenna. Further, it can be very simply tuned by operators for various frequencies to which the antenna is desired to be tuned. No complicated circuits or controls are required and the entire tuning system is made of conventional components.

It is accordingly a primary object of this invention to provide an antenna tuning system that will provide resonance for separate frequencies for either transmission or reception.

It is a further object of this invention to provide an antenna tuning system for the reception or transmission of four or more separate frequencies comprising an inductance and three or more series resonant circuits connected in parallel and a parallel resonant circuit operating as an isolating circuit connected in series between the inductance and the series resonant circuits.

It is still another object of this invention to provide a multiple frequency antenna system that will receive or transmit four or more separate frequencies at resonance in a simply tuned and operated antenna tuning system that can be made from conventional electrical components and which is rugged and stable and easily operated and installed in the field.

Further objects of this invention will appear in the detailed description which follows and will be otherwise apparent to those skilled in the art.

For the purpose of illustration of this invention there is shown in the accompanying drawing a preferred embodiment. It is to be understood that this drawing is for the purpose of example only and that the invention is not limited thereto. This drawing shows an antenna tuning system that will operate on five frequencies, but it will be understood that it can also operate on four or less frequencies where one or more of the series resonant circuits may be deleted or it can operate on more than five frequencies by addition of further series resonant circuits as will be well understood by those skilled in the art.

This drawing is a schematic diagram showing the antenna tuning system connected between the radiating section or" an antenna and a coaxial line adapted to be connected to an automobile radio or other radio, transmitter, receiver or the like.

In the drawing the antenna tuning system of this invention is generally indicated by the reference numeral iii. As there shown it is connected at one side to a radiating section 12 of a conventional short whip antenna. At the other side it is connected to a coaxial cable 14 leading to a radio transmitter through lead 15. The coaxial cable is grounded at 16, such as by connecting to a frame of an automobile or the like where the installation is made in a car.

The antenna tuning system comprises as its major components an inductance coil L1, a parallel resonant circuit T1, and series resonant circuits T2, T3, T4, and T5, connected in series with the capacitor in T1 and the antenna. The coil L1 loads the antenna to resonance on the lowest frequency. The parallel resonance circuit T1 is also tuned to the lowest frequency to offer a high impedance to the four higher frequency tuned circuits, thus avoiding loading effects of circuits T2, T3, T4, and T5 and to isolate these circuits at the lower frequencies. The series resonant circuits T2, T3, T4, and T5 are individually tuned to four separate frequencies with sufficient separation to avoid serious interaction.

The coil L1 and the coil in the parallel resonant circuit T1 may preferably be made from a single coil by the provision of tap 18, thus breaking the coil down into the coil L1 and coil 20' forming the coil in the T1 parallel resonant circuit. A tap 22 is also provided so as to vary the value of coil L1, where desired. The capacitor 24, taken with the coil 20 completes the parallel resonant circuit for circuit T1. For tuning to the lowest frequency, coil L1 and coil 20 in circuit T1 should have high impedance at the higher frequenices and will have negligible effect on the higher frequencies. The capacitor 24 in circuit T1 has low enough impedance to pass the higher frequencies and thus the circuit T1 need not be tuned exactly to the lowest frequency and thereby provides a desired advantage for adaptability and variability.

In the series resonant circuits T2, T3, T4 and T5, the circuits are made up by providing coil 26 and variable capacitance 28 in circuit T2, coil 30 and variable capacitance 32 in circuit T3, coil 34 and variable capacitance 36 in circuit T4, and coil 38 and variable capacitance 40 in circuit T5.

The tuning system above described can very simply be adjusted to the amateur bands at 10, 15, 20, 40 and 80 meters. When so adjusted the antenna may be maintained on resonance and ready to operate on any of these hands by feeding energy into the antenna within the acceptable range. It is, of course, to be understood that the frequencies employed for the operation are not confined to amateur bands.

For purpose of example, the antenna tuning system so described may be employed with the electrical constants described below for operation at the amateur bands of 10, 15, 20, 40 and 80 meters.

It has been found that the following electrical values, provide a very desirable five frequency antenna tuning system. The values listed are for an antenna of 96 inches that can be loaded by the tuning system of this invention to one-quarter wave length. The following electrical values for the five frequencies through the coil L1 and circuit T1, circuit T2, circuit T3, circuit T4, and circuit T5 provide tuning circuits to make up for the difference in the length of the antenna to provide an effective quarter Wave length. Thus, these values provide the desired wave length for the 80 meter band in the coil L1 and in circuit T1, the 40 meter band in circuit T2, the 20 meter band in circuit T3, the meter band in circuit T4, and the 10 meter band in circuit T5. [For the 80 meter band the coil L1 is 80 microhenries, While the coil in circuit T1 is microhenries, and the capacitance 24 is 100 micro-microfarads. For the 40 meter band, in circuit T2 the coil 26 is 17 microhenries while the variable capacitance 28 is from 30 to 48 micromicrofarads. For circuit T3 the 20 meter band, the coil 30 is 8.2 microhenries, while the variable capacitance 32 is 5 to 23 micro-microfarads. For circuit T4 in the 15 meter band, the .coil 34 is 4.1 microhenries while the variable capacitance 36 is from 5 to 23 micro-microfarads. For the 10 meter band in circuit T5, the coil 38 is 1.8 microhenries while the variable capacitance is S to 23 micro-microfarads. The antenna tuning system is connected as previously mentioned to the coaxial cable 14 and the resistance from this connection to ground leading into the automobile radio, or other receiver, as an actual example, provides approximately ohms for this unbalanced line.

By the foregoing description it will be apparent that there has been provided an antenna tuning system that will operate very effectively on five separate frequencies. The use of the isolating circuit T1 makes it possible very desirably to operate at more than three frequencies and, as shown in the example for purpose of illustration, at five frequencies. Additional frequencies can also be employed by providing additional resonant circuits as will be well understood in the art. The provision therefore of the isolating circuit provides an antenna tuning system which can be very desirably employed for the reception or transmission of four or more separate frequencies.

Various changes and modifications may be made in the antenna tuning system of this invention as above described and as will be readily apparent to those skilled in the art. Such changes and modificaions are Within the scope and teaching of this invention as defined by the claims appended hereto.

What is claimed is:

1. A multiple frequency antenna tuning system cooperable with an antenna to provide resonance for separate frequencies, said antenna system comprising a low frequency coil having high impedance to the higher frequencies, a parallel resonant isolating circuit tuned to the lowest frequency and having high impedance to the higher frequencies, and at least three series resonant circuits tuned to separate frequencies, said series resonant circuits being connected to parallel to one another and as a group in series with said parallel resonant circuit, all of said circuits being connected in parallel to said low frequency coil.

2. A multiple frequency antenna tuning system cooperable with an antenna to provide resonance for at least four separate frequencies, said antenna system comprising a low frequency coil having high impedance to the higher frequencies, a parallel resonant isolating circuit comprising an inductance and capacitance connected in parallel and tuned to the lowest frequency and having high impedance to the higher frequencies, and at least three separate series resonant circuits connected in parallel to one another, said series resonant circuit being individually resonant to at least three separate higher frequencies and comprising an inductance and capacitance connected in series, said series resonant circuits being connected as a group in series with the parallel resonant circuit and all of said circuits being connected in parallel to said low frequency coil.

3. The antenna tuning system of claim 2 wherein the antenna is one-quarter wave length or multiples thereof, and all of the capacitances are adjustable to provide for resonance in at least four separate wave length bands.

4. A multiple frequency antenna tuning system cooperable with an antenna to provide resonance for at least four separate frequencies, said antenna system comprising a low frequency coil having high impedance to the higher frequencies, a parallel resonant isolating circuit comprising an inductance and capacitance connected in parallel and tuned to the lowest frequency and having high impedance to the higher frequencies, the low frequency coil and the inductance in the parallel resonant circuit being adjustable in impedance and [formed by providing divider tap means upon a single impedance coil and at least three separate sen'es resonant circuits connected in parallel to one another, said series resonant circuits being individually resonant to at least three separate higher frequencies and comprising an inductance and capacitance connected in series, said series resonant circuits being connected as a group in series with the parallel resonant circuit and all of said circuits being connected in parallel to said low frequency coil.

References Cited in the file of this patent UNITED STATES PATENTS 1,627,767 Brillouin et a1 May 10, 1927 1,656,225 Osnos Jan. 17, 1928 2,005,236 Moullein June 18, 1935 2,321,376 Finch June 8, 1943 2,830,283 Massa Apr. 8, 1958 

4. A MULTIPLE FREQUENCY ANTENNA TUNING SYSTEM COOPERABLE WITH AN ANTENNA TO PROVIDE RESONANCE FOR AT LEAST FOUR SEPARATE FREQUENCIES, SAID ANTENNA SYSTEM COMPRISING A LOW FREQUENCY COIL HAVING HIGH IMPEDANCE TO THE HIGHER FREQUENCIES, A PARALLEL RESONANT INSOLATING CIRCUIT COMPRISING AND INDUCTANCE AND CAPACITANCE CONNECTED IN PARALLEL AND TUNED TO THE LOWEST FREQUENCY AND HAVING HIGH IMPEDANCE TO THE HIGHER FREQUENCIES, THE LOW FREQUENCY COIL AND THE INDUCTANCE IN THE PARALLEL RESONANT CIRCUIT BEING ADJUSTABLE IN IMPEDANCE AND FORMED BY PROVIDING DIVIDER TAP MEANS UPON A SINGLE IMPEDANCE COIL AND AT LEAST THREE SEPARATE SERIES RESONANT CIRCUITS CONNECTED IN PARALLEL TO ONE ANOTHER, SAID SERIES RESONANT CIRCUITS BEING INDIVIDUALLY RESONANT TO AT LEAST THREE SEPARATE HIGHER FREQUENCIES AND COMPRISING AN INDUCTANCE AND CAPACITANCE CONNECTED IN SERIES, SAID SERIES RESONANT CIRCUITS BEING CONNECTED AS A GROUP IN SERIES WITH THE PARALLEL RESONANT CIRCUIT AND ALL OF SAID CIRCUITS BEING CONNECTED IN PARALLEL TO SAID LOW FREQNENCY COIL. 